Cancer is known to have become increasingly important in all countries. Treatment of cancer and therapeutic success depend to a significant extent on prompt detection of the cancer. Therefore, there is a great demand for reliable cancer diagnostic agents, in particular those that allow detection of metastases and micrometastases, even when there are no definite histological findings or when the histological findings are negative.
Colorectal cancer is the second main cause of cancer fatalities; the incidence has been increasing steadily and it often recurs after a curative surgical operation. Colorectal cancer (malignant tumors of the colon and rectum) are occurring in a constantly increasing incidence in industrial countries and constitute the second most common type of cancer in men and the third most common in women. Colorectal cancer constitutes 50% of malignancies. There are more than 200,000 new cases of colorectal cancer each year, and more than 100,000 patients die of it. Colorectal cancer is thus the second leading cause of death due to cancer.
Colorectal cancer may develop de novo or as part of an adenoma-carcinoma sequence in an adenomatous polyp. The probability of a malignancy is between 1% and 40% in the case of adenomas. To this extent, the patients with colorectal polyps constitute a risk group.
For this reason, early detection of colorectal cancer in adenomas and reliable differentiation from benign colorectal tissue are of crucial importance, especially for the prognosis and course of treatment.
Diagnosis and prognosis for this type of cancer are influenced by a variety of properties which are present at the time of the initial diagnosis. These factors include age, sex, duration of symptoms, condition of the intestinal obstruction, tumor localization, the need for a blood transfusion and the quality of the surgical intervention. Although a number of tumor properties such as vascular lymphatic invasiveness, the degree of differentiation and the preoperative titer of conventional tumor markers have shown a prognostic relevance, but there are no suitable markers for detection of early stages of cancer (benign colorectal precursors (adenomas) that become malignant) or for histopathologically unremarkable micrometastases (minimal residual disease) which may be responsible for a recurrence of the carcinoma, even after curative surgical resection. The tumor markers CEA, CK 19 and CK 20 which have been used in the past are indicative of the current prognosis but are unreliable in a differential diagnosis.